Synthesis, crystal structure and Hirshfeld surface analysis of diaquabis(o-phenylenediamine-κ2 N,N′)nickel(II) naphthalene-1,5-disulfonate

In the title salt, [Ni(C6H8N2)2(H2O)2]·(C10H6O6S2), the NiII atom exhibits a slightly tetragonally distorted {O2N4} octahedral coordination environment, with two pairs of equatorial Ni—N bonds and a pair of longer axial Ni—O bonds.

In this work, we focus on the synthesis, crystal structure, and Hirshfeld surface analysis of a nickel(II) complex, [Ni(OPD) 2 (H 2 O) 2 ]•NDS, where the NDS 2-anion is not part of the metal coordination sphere.

Structural commentary
The structures of the molecular entities of the title compound are shown in Fig. 1.This salt consists of an Ni II -centered complex cation with two bidentate OPD ligands and transaligned aqua ligands, as well as of a non-coordinating NDS 2- anion, which is the double-deprotonated form of H 2 NDS.The Ni II atom is situated at a crystallographic inversion center (Wyckoff letter d of space group P2 1 /n) and exhibits a slightly tetragonally distorted {O 2 N 4 } octahedral coordination environment, with two pairs of shorter equatorial Ni-N bonds [2.0775 (17) and 2.0924 (18) A ˚] and a pair of longer axial Ni-O bonds [2.1381 (17) A ˚].The OPD ligand, likewise located over a crystallographic inversion center at the middle of the central C11-C11(À x + 1, À y + 2, À z + 1) bond, is almost coplanar with the NiN 4 plane, with a dihedral angle of 0.95 (9) � .The deviation of the ideal octahedral coordination sphere around nickel might be explained as follows: The inflexible nature of the OPDA ring system with an N� � �N distance between the amino groups of 2.770 (2) A ˚determines the N2-Ni1-N1 and N2-Ni1-N1(À x + 2, À y + 1, À z + 1) bite angles of 83.26 (7) and 96.74 (7) � , respectively.
The supramolecular interactions discussed above were quantitatively investigated and visualized using Hirshfeld surface analysis performed with CrystalExplorer (Spackman et al., 2021), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed color scale of À 0.5408 (red) to 1.4249 (blue) a.u.. Visualizations were performed using a red-white-blue color scheme, where red highlights contacts shorter than the sum of the van der Waals (vdW) radii, white contacts around vdW separations, and blue contacts longer than the sum of the vdW radii.It should be noted that the Hirshfeld surfaces and fingerprint plots were calculated separately for the [Ni(OPD) 2 (H 2 O) 2 ] 2+ cation and the NDS 2- dianion.The d norm surface has twelve bright-red spots on the Hirshfeld surface for the cation and anion each (Fig. 5), resulting from the two O-H� � �O and four N-H� � �O intermolecular hydrogen bonds, as discussed above (Fig. 5; the number is doubled due to inversion symmetry for both enti-ties).The classical O-H� � �O and N-H� � �O hydrogen bonds correspond to H� � �H and H� � �O contacts in the two-dimensional fingerprint plots (with contributions of 44.1 and 50% to the Hirshfeld surface for the [Ni(OPD) 2 (H 2 O) 2 ] 2+ cation and NDS 2-anion, respectively; Fig. 6b and 6f).O� � �H/H� � �O and C� � �H/H� � �C, interactions in the cation, and H� � �H and C� � �H/H� � �C interactions in the dianion follow with contributions of 34.3, 14.8, 25 and 15.3%, respectively (Fig. 6c,d,g,h).Other minor contributions are from C� � �C (6.5%) and C� � �O (0.3%) contacts in the cation, and from C� � �C (8.2%), C� � �O (0.3%), O� � �O (0.1%) and S� � �H (0.1%) contacts in the dianion.The O� � �H/H� � �O contacts are visible as a spike with a sharp tip on the side of the corresponding two-dimensional fingerprint plot, which is indicative of strong intermolecular interactions between atoms.On the other hand, the C� � �H/ H� � �C contacts form less pronounced spikes, suggesting that these interactions are much weaker.

Database survey
In a search of the Cambridge Structural Database (CSD, version 2022.3.0;Groom et al., 2016), a total of 207 compounds containing the o-phenylenediamine moiety were identified.Out of these, 129 compounds were metal complexes, while 78 compounds were organic salts.One organic salt comprising protonated o-phenylenediamine and 1,5-naphthalenedisulfonate has been studied (CSD refcode PEFYOQ; Deng et al., 2012).When searching with 1,5-naphthalenedisulfonic acid as the search criterion, 90 metal complexes and 170 organic salt compounds were found.In the majority of metal complexes, 1,5-naphthalenedisulfonic acid was found in its dianionic form and was not part of the coordination sphere.However, in ten cases a bridging mode for the 1,5naphthalenedisulfonate anion was found.Only one compound was identified where the 1085 Figure 3 Formation of hydrogen bonds (dashed lines) between the NDS 2-anion with six neighboring cations.Symmetry codes refer to Table 1.

Figure 4
The crystal packing of the title salt in a view along [010] based on the formation of O-H� � �O and N-H� � �O hydrogen bonds (dashed blue lines).The coordination sphere around Ni II is given in the polyhedral representation.coordinates to a transition-metal cation (copper) in a monodentate manner (XABPEW; Chen et al., 2002).

Synthesis and crystallization
The starting materials are commercially available and were used without further purification.The ligand OPDA (0.216 g, 2 mmol) was dissolved in 10 ml of a 1:1 v/v ethanol/water mixture.This solution was then added to a solution containing nickel(II) sulfate heptahydrate (0.281 g, 1 mmol) and disodium naphthalene-1,5-disulfonate (0.332 g, 1 mmol) in 10 ml of the same mixed ethanol/water solvent.The resulting mixture was heated under reflux and stirred for 40 min.After 5 d of slow solvent evaporation at room temperature, a lightgreen crystalline product was obtained with a yield of 65%

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were placed in calculated positions and refined using a riding-model approximation, with U iso (H) = 1.2U eq (C) and C-H = 0.93 A for aromatic H atoms. Hydrogen atoms of the amino groups and of the water molecule were located using a difference-Fourier map and refined with bond-length restraints of 0.89 (1) and 0.85 (1) A ˚, respectively.(Rigaku OD, 2023), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), OLEX2 (Dolomanov et al., 2009).Δρ min = −0.49e Å −3 Extinction correction: SHELXL (Sheldrick, 2015a), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0006 (2) Special details Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

Figure 6
Figure 6 Two-dimensional fingerprint plots for the [Ni(OPD) 2 (H 2 O) 2 ] 2+ cation [parts (a), (b), (c) and (d)] and the NDS 2À dianion [parts (e), (f), (g) and (h)].The d i and d e values are the closest internal and external distances (in A ˚) from a given point on the Hirshfeld surface.

Table 2
Experimental details.
Computer programs: CrysAlis PRO